This invention relates to thin walled annealed polymeric articles such as films, a particular embodiment of this invention relates to annealed films filled with high concentrations of platelet type filler to decrease gas and vapor permeability.
It is known that mineral particles can reduce the rate of the diffusion, and hence the permeability of gases and vapors through polymeric materials. The practical application of this effect has not been achieved in film, particularly thin films of low permeability.
Thin films which are resistant to the permeability of gases such as oxygen, and vapors such as water, are useful in packaging of sensitive foods, drugs and chemicals. Typically, the permeability to oxygen as measured by gas transmission rates normalized to one mil (2.54.times.10.sup.-3 cm) thick films at 25.degree. C. should be no higher than about 3.0 cc per 100 square inches (645 cm.sup.2) per day per atmosphere differential across film (measured by ASTM-Test D-1434-75 Method V at 50 psi). The Moisture Vapor Transmission rate (MVT) normalized to one mil (2.54.times.10.sup.-3 cm) thick film should be below 0.5 grams per 100 square inches (645 cm.sup.2) per day (measured according to ASTM-E96 Procedure E) when measured at 100.degree. F. (37.8.degree. C.) with a 90% relative humidity differential across the film. Typically, film used for packaging of foods, drugs and chemicals has a total thickness of less than about 100 micrometers to be economical. Further, such film should permit rapid heat penetration in sealing operations on packaging machines. The films must have sufficient physical properties to withstand the absuse of packaging and shipping operations without cracking.
It is known that plate-like shaped fillers are more effective than rod-like or spherical shaped fillers in lowering the rate of diffusion of gases and vapors through natural rubber, Diffusion of Polymers, Chapter 6, Academic Press, 1968. Great Britain Pat. No. 1,136,358 describes the use of mica in polyethylene or polystyrene to form a 125 micrometer pressed film. Other fillers disclosed in this Great Britain patent include graphite, talc and organic substrates. French Pat. No. 1,299,089 discloses the use of mica in polyvinylidene chloride copolymers to reduce permeability. The use of talc, mica and other fillers in low density polyethylene films is disclosed in a publication by Helsinki University in Polymer Science and Engineering, Jan. 19, 1979. It was noted that low density polyethylene films containing such fillers were brittle when the mineral content was above 30% by weight.
U.S. Pat. No. 4,528,235 discloses that thin polymer films and laminates containing small particle sized platelet type filler. The films are from about 10 to 100 micrometers in thickness. The polymer has a melt index of from 0.01 to 10 grams per 10 minutes at 190.degree. C. to 250.degree. C. as measured on ASTM Test No. D-1238 at a load of 1000 to 2160 grams. The polymer can be any suitable polymer useful for forming thin films, and is preferably a polyamide or a high density polyethylene. There is from 10 to 50 weight percent of a platelet type filler having an average equivalent diameter of about 1 to 8 micrometers. The filler is homogeneously distributed through the film and a plate through the major plane of the filler particles is substantially parallel to the major plane of the film. The substantial parallelism can be determined by X-ray diffraction analysis.